341 research outputs found
Oligocene–Holocene calcareous nannofossil biostratigraphy and diagenetic etch patterns on quaternary placoliths at ODP Site 1139 on Skiff Bank, northern Kerguelen Plateau
No full textThe distribution of calcareous nannofossils at Ocean Drilling Program
Site 1139 on Skiff Bank off the western edge of the Northern Kerguelen
Plateau has been used to delineate Quaternary, middle Miocene–
middle Oligocene, and lower Oligocene sediments in an expanded 385-
m rotary-cored section. Sedimentation rates through most of the Tertiary
are high (average = 23 m/m.y.) as a result of clastic input and dilution
by high siliceous productivity; chert, however, was encountered in
only a single sample. These characteristics, plus the presence of multiple,
reasonably well preserved siliceous and calcareous microfossil
groups deposited well above the calcite compensation depth, make this
site a potential candidate for more detailed coring for paleoceanographic
objectives in the future.
A scanning electron microscope study revealed that diagenetic etching,
apparently of gephyrocapsids, caused some of these placoliths to
superficially resemble Emiliania huxleyi at levels in the Quaternary well
below the evolutionary first occurrence of this taxon. Other larger specimens
of etched gephyrocapsids and/or reticulofenestrids resembled
Pseudoemiliania lacunosa. These observations suggest that caution
should be exercised when age-dating Quaternary sediments not
necessarily rich in carbonate. An unusual Braarudosphaera bloom recorded in upper Oligocene sediments
on Skiff Bank is similar to that reported previously at Site 737 on
the Northern Kerguelen Plateau and may correlate with other such occurrences
of this age in the Atlantic and Indian Oceans. The base of the
pelagic section is dated as earliest Oligocene by nannofossils and foraminifers
(32.8–34.3 Ma; Subchron CP16a/b and basal AP13)
Mesozoic and Cenozoic Calcareous Nannofossils Recovered by DSDP Leg 36 Drilling on the Falkland Plateau, Southwest Atlantic Sector of the Southern Ocean
No full textCorrelation of EoceneOligocene Calcareous Nannofossil Assemblages from Piston Cores Taken in the Vicinity of Deep Sea Drilling Sites 511 and 512, Southwest Atlantic Ocean
No full textMesozoicCenozoic Depositional Environments Revealed by Deep Sea Drilling Project Leg 93 Drilling on the Continental Rise off the Eastern United States: Cruise Summary
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The Geologic and Tectonic Evolution of the Kerguelen Plateau: An Introduction to the Scientific Results of Leg 120
No full textA Preliminary Study of the Evolution of Chiasmolithus in the Middle Eocene to Oligocene of Sites 647 and 748
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Jurassic calcareous nannofossils from prerift sediments drilled during ODP Leg 173, Iberia Abyssal Plain, and their implications for rift tectonics
No full textEocene calcareous nannofossil biostratigraphy and sediment accumulation of turbidite sequences on the Iberia Abyssal Plain, ODP Sites 1067-1069
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